Battery having an adhesive resin layer containing a filler

ABSTRACT

Conventional batteries are disadvantageous in that a firm outer case must be used to maintain an electrical connection between electrodes, which has been an obstacle to size reduction. Those in which each electrode and a separator are joined with an adhesive resin suffer from conflict between adhesive strength and battery characteristics. To solve these problems, it is an object of the invention to provide a battery which requires no outer case so as to realize reduction in thickness and weight and yet exhibits excellence in both battery characteristics and adhesive strength. A positive electrode, a negative electrode, and a separator are joined via an adhesive resin layer having at least one adhesive resin layer containing a filler. The adhesive resin layer has pores, which are filled with an electrolytic solution to exhibit sufficient ion conductivity thereby to improve battery characteristics and to retain adhesive strength.

This application is a 371 of PCT/JP98/00152, filed Jan. 19, 1998.

TECHNICAL FIELD

This invention relates to a battery and, more particularly, to a batterystructure that realizes a light and thin battery having a highdischarging current at a high current density and satisfactory cyclecharacteristics.

BACKGROUND OF THE INVENTION

Batteries have been used long as a main power source or a backup powersource for a variety of equipment. The demand for batteries has recentlybeen increasing with the development of portable electronic equipment,such as cellular phones and portable personal computers. Primarybatteries and secondary batteries are available according to use. As tosecondary batteries having great convenience, high performance batteriessuch as lithium ion secondary batteries and nickel-hydrogen batterieshave been attracting attention. The present invention will hereinafterbe explained by referring to lithium ion secondary batteries the demandof which has been steeply increasing for use in portable electronicequipment.

Conventional lithium ion secondary batteries comprise a battery bodythat is a cylindrical roll of an electrode body or a stack ofrectangular electrode bodies, the electrode body being composed of apositive electrode, a negative electrode, and a separator that isinterposed between the two electrodes to serve for insulation andretention of an electrolyte. The battery body is put in a metal-madecase so that the positive electrode, the negative electrode and theseparator can be brought into intimate contact by the pressure of thecase thereby to maintain the contact between each electrode and theseparator.

An electrical contact can be maintained by putting the battery body in ametal-made case, but there is a problem that the case, being made ofmetal, increases the weight of the battery. Moreover, it is difficult tomake a thin metal case. Difficulty in making a thin case has been agreat obstacle to fulfillment of the demand for batteries to be used incompact portable equipment.

In this connection, U.S. Pat. No. 5,437,692 discloses a structure inwhich a lithium ion-conducting polymer is used as an ion conductinglayer, and a positive electrode and a negative electrode are joined tothe ion-conducting layer with an adhesive layer containing a lithiumcompound. The inventors of the present invention previously proposed inJapanese Patent Application No. 8-338240 a battery structure requiringno metal-made rigid case and a process for producing the same, in whicha positive electrode and a negative electrode are previously joined to aseparator with an adhesive resin.

Bonding positive and negative electrodes to a separator with an adhesiveresin has made it feasible to maintain an electrical contact among themwithout imposing an external force. However, being insulating, innature, an adhesive resin present in the interface between a positiveand a negative electrode and a separator tends to shut an electricalflow, i.e., ion conduction.

In bonding a positive and a negative electrode to a separator with anadhesive resin, the adhesive strength tends to increase with the amountof the adhesive resin in the interface. There is a tendency, however,that battery characteristics are deteriorated with an increasing amountof the adhesive resin. That is, conflict between adhesive strength andbattery characteristics is observed. As the amount of the adhesive resinincreases, the adhesive area tends to increase because the spots of theadhesive resin applied to the interface increase ultimately to form afilm covering the interface. As a result, the adhesive strengthincreases, but, with the interface between electrodes being covered withan insulating film, it seems that ion conducting passages betweenelectrodes are reduced, resulting in deterioration of the batterycharacteristics. Where, on the other hand, the adhesive resinconcentration in a solution type adhesive for bonding is diminished forthe purpose of improving battery characteristics, the adhesive resinsolution having a reduced viscosity penetrates into the electrodes thatare porous only to exhibit low adhesive strength or even fail to bond.It has therefore been a significant theme to improve batterycharacteristics while retaining adhesive strength.

Electrodes have their surfaces smoothed by pressing but still haveunevenness of several microns to form vacancies where a separator andthe electrodes are not in contact. The vacancies that should have beenfilled with an electrolyte may get starved of the electrolyte, whichdepends on the amount of the electrolyte supplied and the condition ofuse of the battery. Starvation of the electrolyte leads to an increaseof internal resistivity of the battery and reductions in batterycharacteristics.

The present invention has been reached, aiming at settlement of theabove-described problems. It is an object of the invention to provide alight and thin battery which has improved battery characteristics whilesecuring adhesive strength.

DISCLOSURE OF THE INVENTION

A first battery according to the invention comprises a battery bodyhaving a positive and a negative electrode containing an activematerial, a separator holding an electrolyte, and an adhesive resinlayer joining the positive and the negative electrodes to the separator,wherein the adhesive resin layer is composed of at least one layer andcontains a filler. According to this structure, the filler added makesthe adhesive resin layer porous. The electrolyte and the adhesive resinsolution can be held in the pores so that satisfactory batterycharacteristics can be obtained while securing adhesive strength.

A second battery according to the invention is the above-described firstbattery, wherein the electrolyte is an organic electrolyte containinglithium ions. This mode, when applied to lithium ion secondary batterieswhich are required to have reduced weight and thickness, provides a highperformance compact battery.

A third battery according to the invention is the above-described firstbattery, wherein the average particle size of the filler is equal to orsmaller than the particle size of the active material of the positiveand negative electrodes. According to this mode, the adhesive resinsolution is held by the adhesive resin layer to give necessary adhesivestrength.

A fourth battery according to the invention is the above-described firstbattery, wherein the average particle size of the filler is 1 μm orsmaller. According to this embodiment, the filler manifests a properthickening effect for the adhesive resin solution and makes the adhesiveresin layer porous thereby to secure satisfactory batterycharacteristics while retaining adhesive strength.

A fifth battery according to the invention is the above-described firstbattery, wherein the sum of a volume ratio of the adhesive resin andthat of the filler per unit volume of the adhesive resin layer is lessthan 1. This mode secures the porosity of the formed adhesive resinlayer.

A sixth battery according to the invention is the above-described firstbattery, wherein the sum of a volume ratio of the adhesive resin andthat of the filler per unit volume of the adhesive resin layer is 0.2 to0.8. According to this embodiment, the voids of the porous adhesiveresin are filled with the electrolyte to exhibit sufficient ionconductivity.

A seventh battery according to the invention is the above-describedfirst battery, wherein the filler comprises at least one ofnon-conductive materials and semiconductors. According to this mode, theadhesive resin layer can be made porous to provide satisfactory batterycharacteristics while retaining adhesive strength.

An eighth battery according to the invention is the above-describedfirst battery, wherein the adhesive resin layer comprises a layercontaining an electrically conductive filler and a layer containing atleast one of non-conductive materials and semiconductors. According tothis embodiment, the conductive filler-containing layer functions todiminish the internal resistivity of the battery.

A ninth battery according to the invention is the above-described firstbattery, wherein the adhesive resin layer is constituted so as to fillthe vacancies formed in the interface between each electrode and theseparator due to the unevenness of the electrode and the separator. Thisstructure is effective in increasing the adhesive strength andpreventing reduction of battery characteristics due to starvation of theelectrolyte.

A tenth battery according to the invention is the above-described firstbattery, wherein the battery body is a laminate of a plurality ofelectrode bodies each composed of a single layer of the positiveelectrode, a single layer of the separator, and a single layer of thenegative electrode.

An eleventh battery according to the invention is the above-describedtenth battery, wherein the laminate is formed by interposing thepositive electrode and the negative electrode alternately among aplurality of the separators.

A twelfth battery according to the invention is the above-describedtenth battery, wherein the laminate is formed by interposing thepositive electrode and the negative electrode alternately between rolledseparators.

A thirteenth battery according to the invention is the above-describedtenth battery, wherein the laminate is formed by interposing thepositive electrode and the negative electrode alternately between foldedseparators.

The tenth to thirteenth embodiments are effective in providing alaminated electrode type battery having high performance and a highbattery capacity.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram showing the volume ratio in the adhesive resin layerof the battery according to the invention.

FIG. 2 is a schematic cross-sectional view showing the space formed inthe interface between an electrode and a separator in the batteryaccording to the invention.

FIG. 3 is a graph showing the change in discharge capacity brought aboutby addition of an alumina filler to a PVDF resin.

FIG. 4 is a graph showing the change in discharge capacity caused byaddition of an alumina filler to a PVA resin.

FIG. 5 is a graph showing the relationship between peel strength anddischarge capacity with an alumina filler added having a varied averageparticle size.

FIG. 6 is a graph showing the relationship between peel strength anddischarge capacity against volume percentage of the voids of an adhesiveresin layer.

FIG. 7 is a graph showing the relationship between peel strength anddischarge capacity against thickness of an adhesive resin layer.

THE BEST MODE FOR CARRYING OUT THE INVENTION

The modes for carrying out the invention are hereinafter described byreferring to the drawings.

Where a positive and a negative electrode are bonded to a separator withan adhesive resin, ion conductivity is lessened to deteriorate batterycharacteristics according as the amount of the adhesive resin isincreased for strengthening the adhesion. This is because the adhesiveresin layer is formed in a film to block the passages for ion migration.Therefore, the problem ought to be solved only if the adhesive resin isnot filmy but porous. The present invention consists in incorporating afiller into the adhesive resin so as to make the adhesive resin layerporous.

If an adhesive resin solution containing no filler is applied to anelectrode or a separator for bonding, the adhesive resin solution willbe absorbed by the adherents, particularly the electrode that is porous.Where a filler is mixed into the adhesive resin solution, the adhesiveresin itself is given a porous structure by the filler to provide pores.Since the adhesive resin solution is held in the pores and therebyprevented from being absorbed by the electrode, the adhesive resinsolution can be retained on the adherend surface. Further, this effectbrings about an increase in viscosity of the adhesive resin solution tofurther improve adhesive holding properties.

The average particle size of the filler to be added is preferably notgreater than that of the electrode active material, particularly 1 μm orsmaller. Filler particles having an average particle size of greaterthan 1 μm form pores the diameter of which approximates the pore size ofthe electrode, and the ability of holding the electrolytic solutiondecreases. Where filler particles have an average particle size equal toor greater than the particle size of the active material, the pores losethe ability of holding the electrolyte, resulting in reductions ofbattery characteristics. That is, the filler added produces nosubstantial effect. The sedimentation velocity of the filler particlesincreases with an increasing average particle size, which considerablydeteriorates the handling properties of the adhesive resin solution.With the average particle size being 1 μm or smaller, the fillermoderately increases the viscosity of the adhesive resin solution andmakes the adhesive resin layer porous. The adhesive resin solution andthe electrolytic solution can thus be held in the electrode/separatorinterface.

The preference for the above-specified particle size of the fillerapplies to the particles constituting the most part of the filler. Itdoes not matter if the filler contains particles out of that range.

An adhesive resin solution using a solution type adhesive resin is madeup of a filler, an adhesive resin, and a solvent. Since the solvent isremoved on drying, the adhesive resin layer is composed of the filler,the adhesive resin, and the voids formed on solvent's drying. Theconstitution of the adhesive resin layer is illustrated in FIG. 1. Ascan be seen from FIG. 1, the void volume formed by the filler is made upof the volume of the adhesive resin and the volume of the voids formedon solvent's drying. If all the void volume formed by the filler isfilled with the adhesive resin, the adhesive resin layer fails to retainits porosity and becomes an insulating layer. Hence, the sum of a volumeratio of the adhesive resin and that of the filler per unit volume ofthe adhesive resin layer should be less than 1.

In order for the adhesive resin layer to retain porosity, it is requiredas stated above that the sum of a volume ratio of the adhesive resin andthat of the filler per unit volume of the adhesive resin layer be lessthan 1. On the other hand, in order for the voids of the porous adhesiveresin to be filled with an electrolytic solution to exhibit sufficiention conductivity, it is desirable for the adhesive resin layer to haveapproximately the same void volume as the separator used. From thisstandpoint, the sum of a volume ratio of the adhesive-resin and that ofthe filler per unit volume of the adhesive resin layer should be 0.2 to0.8. In other words the volume percentage of the voids based on theadhesive resin layer should be 20% to 80%.

The filler is not particularly limited in material as far as theabove-specified average particle size can be realized. Inorganicsubstances such as oxides, e.g., Al₂O₃, SiO₂, ZrO₂, and LiAlO₂,carbides, e.g., SiC, B₄C, and ZrC, and nitrides, e.g., SiN, BN, and TiN,are stable in an electrolyte and, because they have low conductivity,there is no fear of a short circuit in case the adhesive resincontaining the filler should be present to connect the electrodes.Polymers such as polyolefin resins have not only low conductivity but asmall specific gravity, they are effective in minimizing an increase ofweight as compared with inorganic fillers or metallic fillers.

An inorganic salt, such as LiPF₆ or LiClO₄, that does not dissolve in anelectrolytic solution or remains undissolved can serve as a filler toform fine pores. Even where the inorganic salt dissolves in anelectrolytic solution, it leaves pores in the adhesive resin layer afterdissolving, making it possible to increase the porosity of the adhesiveresin layer.

Where a conductive filler, such as carbon or metal, is used, theadhesive resin layer is endowed with electrical conductivity. Theadhesive resin layer thus having conductivity, electron conduction isnot hindered even if the adhesive resin enters the interstices of anelectrode. However, use of such a conductive material as carbonnecessitates some manipulation for prevention of a short circuit. Ashort circuit can be prevented by, for example, joining an electrode anda separator via a double-layered adhesive resin layer composed of anadhesive resin layer containing a conductive material that is in contactwith the electrode and an adhesive resin layer containing inorganicmatter that is in contact with the separator.

Where the space existing in the electrode/separator interface is filledwith the filler-containing adhesive resin, the adhesive strengthincreases, and reduction in battery characteristics due to shortage ofthe electrolyte can be prevented. Because the surface of an electrodehas not a little unevenness on the order of several microns, it isdesirable that the filler-containing adhesive resin be present so as tofill the gap as shown in FIG. 2. Supposing an allowable reduction indischarge capacity due to resistance of the adhesive resin layer is upto 50%, a desirable thickness of the adhesive resin layer is 50 μm orsmaller. In order to minimize the reduction in discharge capacity, amore desirable thickness of the adhesive resin layer is 10 μm orsmaller.

While the shape of the filler to be added to the adhesive resin is notparticularly limited, it includes a spherical shape, an ellipticalshape, a fibrous shape, and a flaky shape. A spherical filler willachieve an increased packing density, making the adhesive resin layerthinner. An elliptical, fibrous or flaky filler has an increasedspecific surface area to increase the void volume of the adhesive resinlayer.

While the adhesive resin is not particularly limited in kind, materialswhich, when present in battery materials, are not corroded by anelectrolyte or an electrode-forming material and are capable ofretaining adhesiveness are preferred. In particular, adhesive resins ofsolution type are more effective, for the adhesive resin layer caneasily be made porous. In lithium ion secondary batteries containing anorganic electrolyte, fluorocarbon resins represented by polyvinylidenefluoride (PVDF) and polymers containing polyvinyl alcohol in themolecular structure thereof, represented by polyvinyl alcohol, arepreferred.

While not limiting, the adhesive resin is preferably applied in a manneragreeable with a desired thickness and a coating form. Illustrativeexamples of coating methods include screen printing, bar coating, rollcoating, gravure coating, and doctor blade coating.

The invention does not impose particular restriction on the structure ofbatteries to which the invention is applied. The invention is applicableto batteries having a battery body comprising a positive electrode, anegative electrode, a separator, and an adhesive resin layer joining thepositive and the negative electrodes to the separator. Accordingly, thebattery body can be an electrode body composed of a single positiveelectrode layer, a single separator, and a single negative electrodelayer (hereinafter referred to as a unit electrode body) or a laminatedbattery body comprising a plurality of such unit electrode bodies. Whenthe invention is applied to a battery having such a laminated batterybody, there is provided a battery having high performance and a highbattery capacity.

The laminated battery body can be formed by laying a plurality ofpositive electrodes, separators, and negative electrodes all cut insizes or by rolling or folding one or more than one continuous sets of apositive electrode, a separator, and a negative electrode.

The present invention is especially effective when applied to lithiumsecondary batteries, which is not limiting the application of theinvention. The invention is also applicable to primary batteries, suchas lithium primary batteries, manganese-zinc batteries, and silver-zincbatteries; and other types of secondary batteries, such asnickel-cadmium batteries, nickel-zinc batteries, nickel-hydrogenbatteries, polymer batteries, and carbon secondary batteries.

The details of the invention will now hereinafter be given by way ofExamples, but the invention is by no means limited thereto.

EXAMPLE 1 Preparation of Electrode Body

A positive electrode active material layer consisting of 91 parts byweight of LiCoO₂ having an average particle size of 10 μm (produced byNippon Chemical Industrial Co., Ltd.), 6 parts by weight of graphitepowder (produced by Lonza Ltd.), and 3 parts by weight of polyvinylidenefluoride (produced by Kureha Chemical Industry Co., Ltd.) was applied toan aluminum foil substrate to an average coating thickness of 80 μm toform a positive electrode. A negative electrode active material layerconsisting of 90 parts by weight of mesophase microbeads (produced byOsaka Gas Co., Ltd.) having an average particle size of 8 μm and 10parts by weight of polyvinylidene fluoride was applied to a coppersubstrate to an average coating thickness of 80 μm to form a negativeelectrode. An adhesive resin solution for joining these electrodes to apolypropylene/polyethylene/polypropylene three-layered separator(produced by Hoechst Celanese Corporation) was prepared by dispersingand dissolving polyvinylidene fluoride (produced by Elf Atochem Japan)and alumina powder having an average particle size of 0.01 μm (producedby Degussa Corporation) in a concentration of 10 wt % each inN-methylpyrrolidone. The positive electrode, the negative electrode, andthe separator were cut in sizes of 50 mm×50 mm, 55 mm×55 mm, and 60mm×60 mm, respectively. Both sides of the cut piece of the separatorwere coated with the adhesive resin solution on a screen printingmachine using a 300 mesh screen, and the cut positive electrode and thecut negative electrode were stuck thereto. The laminate was dried in adrier at 80° C. for 1 hour to prepare a unit electrode body. Evaluationof electrode body:

1) Measurement of adhesive strength (peel strength)

The adhesive strength between the negative electrode and the separatorof the resulting electrode body was measured by a peel test at 180°.

2) Measurement of battery characteristics

The resulting electrode body, with a current collecting tab spot-weldedto the positive and the negative electrodes thereof, was put in a bagmade of an aluminum laminate sheet. An electrolytic solution was pouredinto the bag, and the opening of the bag was sealed to complete abattery. The battery was charged and discharged at 1C, and a dischargecapacity was measured as a battery characteristic.

Comparative Example 1

Electrodes were prepared, a battery was assembled, and evaluation wasmade in the same manner as in Example 1, except for using an adhesiveresin solution prepared by dissolving polyvinylidene fluoride (PVDF) inN-methylpyrrolidone (NMP) in a concentration of 10 wt %.

EXAMPLE 2

Electrodes were prepared, a battery was assembled, and evaluation wasmade in the same manner as in Example 1, except for using an adhesiveresin solution prepared by dissolving 2 wt % of polyvinyl alcohol and 5wt % of alumina powder having an average particle size of 0.01 μm inN-methylpyrrolidone.

Comparative Example 2

Electrodes were prepared, a battery was assembled, and evaluation wasmade in the same manner as in Example 2, except for using an adhesiveresin solution prepared by dissolving 2 wt % of polyvinyl alcohol inN-methylpyrrolidone.

EXAMPLE 3

Electrodes were prepared, a battery was assembled, and evaluation wasmade in the same manner as in Example 1, except for using an adhesiveresin solution prepared by dissolving and dispersing 10 wt % ofpolyvinylidene fluoride and 10 wt % of alumina powder having an averageparticle size of 0.1 μm in N-methylpyrrolidone.

EXAMPLE 4

Electrodes were prepared, a battery was assembled, and evaluation wasmade in the same manner as in Example 1, except for using an adhesiveresin solution prepared by dissolving and dispersing 10 wt % ofpolyvinylidene fluoride and 10 wt % of alumina powder having an averageparticle size of 1 μm in N-methylpyrrolidone.

EXAMPLE 5

Electrodes were prepared, a battery was assembled, and evaluation wasmade in the same manner as in Example 1, except for using an adhesiveresin solution prepared by dissolving and dispersing 10 wt % ofpolyvinylidene fluoride and 10 wt % of silica powder having an averageparticle size of 0.007 μm in N-methylpyrrolidone.

Comparative Example 3

Electrodes were prepared, a battery was assembled, and evaluation wasmade in the same manner as in Example 1, except for using an adhesiveresin solution prepared by dissolving and dispersing 10 wt % ofpolyvinylidene fluoride and 10 wt % of alumina powder having an averageparticle size of 10 μm in N-methylpyrrolidone.

EXAMPLE 6

Electrodes were prepared, a battery was assembled, and evaluation wasmade in the same manner as in Example 1, except for using an adhesiveresin solution prepared by dissolving and dispersing 10 wt % ofpolyvinylidene fluoride and 5 wt % of alumina powder having an averageparticle size of 0.01 μm in N-methylpyrrolidone.

EXAMPLE 7

Electrodes were prepared, a battery was assembled, and evaluation wasmade in the same manner as in Example 1, except for using an adhesiveresin solution prepared by dissolving and dispersing 5 wt % ofpolyvinylidene fluoride and 25 wt % of alumina powder having an averageparticle size of 0.01 μm in N-methylpyrrolidone.

Comparative Example 4

Electrodes were prepared, a battery was assembled, and evaluation wasmade in the same manner as in Example 1, except for using an adhesiveresin solution prepared by dissolving and dispersing 10 wt % ofpolyvinylidene fluoride and 1 wt % of alumina powder having an averageparticle size of 0.01 μm in N-methylpyrrolidone.

Comparative Example 5

Electrodes were prepared, a battery was assembled, and evaluation wasmade in the same manner as in Example 1, except for using an adhesiveresin solution prepared by dissolving and dispersing 3 wt % ofpolyvinylidene fluoride and 30 wt % of alumina powder having an averageparticle size of 0.01 μm in N-methylpyrrolidone.

EXAMPLE 8

Electrodes were prepared, a battery was assembled, and evaluation wasmade in the same manner as in Example 1, except for using an adhesiveresin solution prepared by dissolving and dispersing 10 wt % ofpolyvinylidene fluoride and 10 wt % of alumina powder having an averageparticle size of 0.01 μm in N-methylpyrrolidone and using a 250 meshscreen for applying the adhesive resin solution.

EXAMPLE 9

Electrodes were prepared, a battery was assembled, and evaluation wasmade in the same manner as in Example 1, except for using an adhesiveresin solution prepared by dissolving and dispersing 10 wt % ofpolyvinylidene fluoride and 10 wt % of alumina powder having an averageparticle size of 0.01 μm in N-methylpyrrolidone and using a 200 meshscreen for applying the adhesive resin solution.

EXAMPLE 10

Electrodes were prepared, a battery was assembled, and evaluation wasmade in the same manner as in Example 1, except for using an adhesiveresin solution prepared by dissolving and dispersing 10 wt % ofpolyvinylidene fluoride and 10 wt % of alumina powder having an averageparticle size of 0.01 μm in N-methylpyrrolidone and using a 100 meshscreen for applying the adhesive resin solution.

Comparative Example 6

Electrodes were prepared, a battery was assembled, and evaluation wasmade in the same manner as in Example 1, except that an adhesive resinsolution prepared by dissolving and dispersing 10 wt % of polyvinylidenefluoride and 10 wt % of alumina powder having an average particle sizeof 0.01 μm in N-methylpyrrolidone was used and that the adhesive resinsolution was applied twice using a 50 mesh screen in screen printing.

EXAMPLE 11

Electrodes were prepared, a battery was assembled, and evaluation wasmade in the same manner as in Example 1, except for using an adhesiveresin solution prepared by dissolving and dispersing 10 wt % ofpolyvinylidene fluoride and 10 wt % of silica powder having an averageparticle size of 0.01 μm (produced by Aerosil Co., Ltd.) inN-methylpyrrolidone.

EXAMPLE 12

Electrodes were prepared, a battery was assembled, and evaluation wasmade in the same manner as in Example 1, except for using an adhesiveresin solution prepared by dissolving and dispersing 10 wt % ofpolyvinylidene fluoride and 30 wt % of silicon carbide powder having anaverage particle size of 0.5 μm (produced by Seimi Chemical Co., Ltd.)in N-methylpyrrolidone.

EXAMPLE 13

Electrodes were prepared, a battery was assembled, and evaluation wasmade in the same manner as in Example 1, except for using an adhesiveresin solution prepared by dissolving and dispersing 10 wt % ofpolyvinylidene fluoride and 30 wt % of boron carbide powder having anaverage particle size of 0.5 μm (produced by Seimi Chemical Co., Ltd.)in N-methylpyrrolidone.

EXAMPLE 14

Electrodes were prepared, a battery was assembled, and evaluation wasmade in the same manner as in Example 1, except for using an adhesiveresin solution prepared by dissolving and dispersing 10 wt % ofpolyvinylidene fluoride and 30 wt % of silicon nitride powder having anaverage particle size of 0.5 μm (produced by Seimi Chemical Co., Ltd.)in N-methylpyrrolidone.

EXAMPLE 15

Electrodes were prepared, a battery was assembled, and evaluation wasmade in the same manner as in Example 1, except for using an adhesiveresin solution prepared by dissolving and dispersing 10 wt % ofpolyvinylidene fluoride and 5 wt % of polymethyl methacrylate (PMMA)powder having an average particle size of 0.5 μm in N-methylpyrrolidone.

EXAMPLE 16

Electrodes were prepared, a battery was assembled, and evaluation wasmade in the same manner as in Example 1, except for using an adhesiveresin solution prepared by dissolving and dispersing 10 wt % ofpolyvinylidene fluoride and 20 wt % of iron powder having an averageparticle size of 0.5 μm in N-methylpyrrolidone.

EXAMPLE 17

Electrodes were prepared, a battery was assembled, and evaluation wasmade in the same manner as in Example 1, except for using an adhesiveresin solution prepared by dissolving and dispersing 10 wt % ofpolyvinylidene fluoride and 50 wt % of carbon powder having an averageparticle size of 1 μm (produced by Osaka Gas Co., Ltd.) inN-methylpyrrolidone.

EXAMPLE 18

Electrodes were prepared, a battery was assembled, and evaluation wasmade in the same manner as in Example 1, except for using an adhesiveresin solution prepared by dissolving and dispersing 10 wt % ofpolyvinylidene fluoride, 9 wt % of alumina powder having an averageparticle size of 0.01 μm, and 1 wt % of alumina powder having an averageparticle size of 1 μm in N-methylpyrrolidone.

EXAMPLE 19

Electrodes were prepared, a battery was assembled, and evaluation wasmade in the same manner as in Example 1, except for using an adhesiveresin solution prepared by dissolving and dispersing 10 wt % ofpolyvinylidene fluoride, 5 wt % of alumina powder having an averageparticle size of 0.01 μm, and 5 wt % of silica powder having an averageparticle size of 0.01 μm in N-methylpyrrolidone.

EXAMPLE 20

Electrodes were prepared, a battery was assembled, and evaluation wasmade in the same manner as in Example 1, except for using an adhesiveresin solution prepared by dissolving and dispersing 10 wt % ofpolyvinylidene fluoride, 9 wt % of alumina powder having an averageparticle size of 0.01 μm, and 1 wt % of silica powder having an averageparticle size of 0.5 μm in N-methylpyrrolidone.

EXAMPLE 21

Electrodes were prepared, a battery was assembled, and evaluation wasmade in the same manner as in Example 1, except for using an adhesiveresin solution prepared by dissolving and dispersing 10 wt % ofpolyvinylidene fluoride, 9 wt % of alumina powder having an averageparticle size of 0.01 μm, and 1 wt % of polymethyl methacrylate (PMMA)powder having an average particle size of 0.5 μm in N-methylpyrrolidone.

EXAMPLE 22

Electrodes were prepared, a battery was assembled, and evaluation wasmade in the same manner as in Example 1, except for using an adhesiveresin solution prepared by dissolving and dispersing 10 wt % ofpolyvinylidene fluoride, 9 wt % of alumina powder having an averageparticle size of 0.01 μm, and 1 wt % of iron powder having an averageparticle size of 0.5 μm in N-methylpyrrolidone.

EXAMPLE 23

Electrodes were prepared, a battery was assembled, and evaluation wasmade in the same manner as in Example 1, except for using an adhesiveresin solution prepared by dissolving and dispersing 10 wt % ofpolyvinylidene fluoride, 9 wt % of alumina powder having an averageparticle size of 0.01 μm, and 1 wt % of carbon powder having an averageparticle size of 1 μm in N-methylpyrrolidone.

EXAMPLE 24

Electrodes were prepared, a battery was assembled, and evaluation wasmade in the same manner as in Example 1, except for using an adhesiveresin solution prepared by dissolving and dispersing 10 wt % ofpolyvinylidene fluoride, 9 wt % of alumina powder having an averageparticle size of 0.01 μm, and 1 wt % of alumina powder having an averageparticle size of 0.5 μm in N-methylpyrrolidone.

EXAMPLE 25

Electrodes were prepared, a battery was assembled, and evaluation wasmade in the same manner as in Example 1, except for using an adhesiveresin solution prepared by dissolving and dispersing 10 wt % ofpolyvinylidene fluoride, 5 wt % of silicon carbide powder having anaverage particle size of 0.5 μm, and 5 wt % of polymethyl methacrylatepowder having an average particle size of 0.5 μm in N-methylpyrrolidone.

EXAMPLE 26

Electrodes were prepared, a battery was assembled, and evaluation wasmade in the same manner as in Example 1, except for using an adhesiveresin solution prepared by dissolving and dispersing 10 wt % ofpolyvinylidene fluoride, 5 wt % of iron powder having an averageparticle size of 0.5 μm, and 5 wt % of polymethyl methacrylate powderhaving an average particle size of 0.5 μm in N-methylpyrrolidone.

EXAMPLE 27

Electrodes were prepared, a battery was assembled, and evaluation wasmade in the same manner as in Example 1, except for using an adhesiveresin solution prepared by dissolving and dispersing 10 wt % ofpolyvinylidene fluoride, 5 wt % of carbon powder having an averageparticle size of 0.5 μm, and 5 wt % of polymethyl methacrylate powderhaving an average particle size of 0.5 μm in N-methylpyrrolidone.

EXAMPLE 28

A positive electrode, a negative electrode, and an adhesive resinsolution were prepared in the same manner as in Example 1. The positiveelectrode, the negative electrode, and a separator were cut in pieces of50 mm×50 mm, 55 mm×55 mm, and 120 mm×60 mm, respectively. The adhesiveresin solution was applied to one side of the cut sheet of the separatoron a screen printing machine. The separator was folded in two with a cutpiece of the negative electrode inserted into the center of the fold andpassed through a two-roll laminator to prepare a negative electrode withseparators. The adhesive resin solution was applied to one of theseparator surfaces having the negative electrode therein, and a cutpiece of the positive electrode was adhered thereto. The adhesive resinsolution was applied to a side of another folded separator having a cutpiece of the negative electrode interposed therein, and the coatedseparator was stuck to the previously adhered positive electrode. Thesesteps were repeated 6 times to build up a laminated battery body. Thebattery body was dried while applying pressure to obtain a tabularlaminated battery body having positive and negative electrodes bonded tothe separators. The battery characteristics of the resulting batterybody were evaluated in the same manner as in Example 1.

EXAMPLE 29

A positive electrode, a negative electrode, and an adhesive resinsolution were prepared in the same manner as in Example 1. The positiveelectrode, the negative electrode, and a separator were cut in pieces of50 mm×50 mm, 55 mm×55 mm, and 120 mm×60 mm, respectively. The adhesiveresin solution was applied to a side of the cut sheet of the separatoron a screen printing machine. The separator was folded in two with a cutpiece of the positive electrode inserted into the center of the fold andpassed through a two-roll laminator to prepare a positive electrode withseparators. The adhesive resin solution was applied to one of theseparator surfaces having the positive electrode therein, and a cutpiece of the negative electrode was adhered thereto. The adhesive resinsolution was applied to a side of another folded separator having a cutpiece of the positive electrode interposed therein, and the coatedseparator was stuck to the previously adhered negative electrode. Thesesteps were repeated 6 times to build up a laminated battery body. Thebattery body was dried while applying pressure to obtain a tabularlaminated battery body having positive and negative electrodes bonded toseparators. The battery characteristics of the resulting battery bodywere evaluated in the same manner as in Example 1.

EXAMPLE 30

A positive electrode, a negative electrode, and an adhesive resinsolution were prepared in the same manner as in Example 1. The positiveelectrode, the negative electrode, and a separator were cut in sizes of300 mm×50 mm, 305 mm×55 mm, and 620 mm×60 mm, respectively. The adhesiveresin solution was applied to a side of a cut sheet of the separator ona screen printing machine. The separator was folded in two with a cutsheet of the negative electrode inserted into the center of the fold andpassed through a two-roll laminator to prepare a negative electrode ofband form with a separator on both sides thereof. The adhesive resinsolution was applied to one of the separator surfaces having thenegative electrode therein, and one end of the negative electrode withseparators was folded back at a prescribed length with a cut sheet ofthe positive electrode inserted into the fold. Subsequently, thepositive electrode and the negative electrode with separators weresuperposed and passed through the laminator. The adhesive resin solutionwas applied to the other separator on the side opposite to the sidepreviously coated with the adhesive resin solution, and the laminate wasrolled up into an oblong cylinder.

The rolled oblong battery body was dried while applying pressure toobtain a tabular roll type battery body having positive and negativeelectrodes bonded to separators. The battery characteristics of theresulting battery body were evaluated in the same manner as in Example1.

EXAMPLE 31

A positive electrode, a negative electrode, and an adhesive resinsolution were prepared in the same manner as in Example 1. The positiveelectrode, the negative electrode, and a separator were cut in sizes of300 mm×50 mm, 305 mm×55 mm, and 620 mm×60 mm, respectively. The adhesiveresin solution was applied to one side of the separator on a screenprinting machine. The separator was folded in two with a cut sheet ofthe positive electrode inserted into the center of the fold and passedthrough a two-roll laminator to prepare a positive electrode with aseparator on both sides thereof. The adhesive resin solution was appliedto one of the separator surfaces having the positive electrode therein,and one end of the positive electrode with separators was folded back ata prescribed length with a cut sheet of the negative electrode insertedinto the fold. Subsequently, the negative electrode and the positiveelectrode with separators were superposed and passed through thelaminator. The adhesive resin solution was applied to the otherseparator on the side opposite to the side previously coated with theadhesive resin solution, and the laminate was rolled up into an oblongcylinder.

The rolled oblong battery-body was dried while applying pressure toobtain a tabular roll type battery body having positive and negativeelectrodes bonded to separators. The battery characteristics of theresulting battery body were evaluated in the same manner as in Example1.

EXAMPLE 32

A positive electrode, a negative electrode, and an adhesive resinsolution were prepared in the same manner as in Example 1. The positiveelectrode, the negative electrode, and a separator were cut in sizes of300 mm×50 mm, 305 mm×55 mm, and 310 mm×60 mm, respectively. A pair ofcut bands of the separator were arranged over both sides of a cut bandof the negative electrode, and a cut sheet of the positive electrode wasarranged on the outer side of one of the separators. The adhesive resinsolution had been applied to both sides of the separator positionedbetween the negative electrode and the positive electrode and the sideof the other separator that was facing the negative electrode. Precededby a prescribed length of the positive electrode, the positiveelectrode, the separators, and the negative electrode were superposedand passed through a laminator to form a laminate of band form. Theseparator surface of the laminate band was coated with the adhesiveresin solution. The sticking end of the positive electrode was foldedback on the coated side, and the laminate was rolled up into an oblongcylinder in such a manner that the folded part might be wrapped in.

The rolled oblong battery body was dried while applying pressure toobtain a tabular roll type battery body having positive and negativeelectrodes bonded to separators. The battery characteristics of theresulting battery body were evaluated in the same manner as in Example1.

EXAMPLE 33

A positive electrode, a negative electrode, and an adhesive resinsolution were prepared in the same manner as in Example 1. The positiveelectrode, the negative electrode, and a separator were cut in sizes of300 mm×50 mm, 305 mm×55 mm, and 310 mm×60 mm, respectively. A pair ofcut bands of the separator were arranged over both sides of a cut bandof the positive electrode, and a cut sheet of the negative electrode wasarranged on the outer side of one of the separators. The adhesive resinsolution was applied to both sides of the separator positioned betweenthe negative electrode and the positive electrode and the side of theother separator that was facing the positive electrode. Preceded by aprescribed length of the negative electrode, the positive electrode, theseparators, and the negative electrode were superposed and passedthrough a laminator to form a laminate of band form- The separatorsurface of the laminate band was coated with the adhesive resinsolution. The sticking end of the negative electrode was folded back onthe coated side, and the laminate was rolled up into an oblong cylinderin such a manner that the folded part might be wrapped in.

The rolled oblong battery body was dried while applying pressure toobtain a tabular roll type battery body having positive and negativeelectrodes bonded to separators. The battery characteristics of theresulting battery body were evaluated in the same manner as in Example1.

The adhesive strength of the prepared electrodes and the dischargecapacity in charging and discharging the prepared batteries at 1C areshown in Tables 1 through 7. The graphs of discharge capacity vs.charging and discharging current with different adhesive resins areshown in FIGS. 3 and 4. Comparisons between Example 1 and ComparativeExample 1 and between Example 2 and Comparative Example 2 reveal thataddition of a filler to an adhesive resin solution brings aboutimprovement in discharge capacity, especially under a high load.

TABLE 1 Adhesive Particle Peel Discharge Weight Size of StrengthCapacity Resin Filler Ratio Filler (gf/cm) (1C) (mAh) Example 1 PVDFalumina 1:1 0.01 50 60 Compara. PVDF none — — 100 20 Example 1 Example 2PVA alumina 2:5 0.01 70 60 Compara. PVA none — — 100 30 Example 2

Table 2 shows the results obtained with the average particle size of analumina filler varied and the results obtained with a silica fillerhaving a smaller particle size. These results are shown in FIG. 5, inwhich the peel strength and the discharge capacity are plotted againstthe particle size of the alumina filler added. FIG. 5 shows that thepeel strength somewhat decreases at a particle size of 1 μm or smaller,which was not problematical for practical use. It is also seen that, onthe other hand, the discharge capacity tends to decrease as the averageparticle size becomes greater than 1 μm because of reduction of voidvolume in the adhesive resin layer.

TABLE 2 Adhesive Particle Peel Discharge Weight Size of StrengthCapacity Resin Filler Ratio Filler (gf/cm) (1C) (mAh) Example 1 PVDFalumina 1:1 C,18 0.01 50 60 Example 3 PVDF alumina 1:1 0.1 60 55 Example4 PVDF alumina 1:1 1 65 50 Example 5 PVDF silica 1:1 0.007 45 60Compara. PVDF alumina 1:1 10 60 25 Example 3

Table 3 shows the results obtained when the ratio of the alumina fillerto the adhesive resin was varied. These results are graphed in FIG. 6,in which the peel strength and the battery capacity are plotted againstvolume percentage of the voids. The proportion of the adhesive resin inthe void volume formed by the filler changes with a change of the fillerto resin ratio, and a change of the void volume in the adhesive resinlayer follows. If the volume percentage of the voids is less than 20%,passages for ions through the adhesive resin layer are diminished,resulting in an obvious reduction in discharge capacity. On the otherhand, the adhesive strength tends to reduce with an increase of volumepercentage of the voids. If the volume percentage of the voids is morethan 80%, the amount of the filler is so large that the amount of theadhesive resin is insufficient, resulting in an extreme reduction inadhesive strength.

Table 4 shows the results obtained when the thickness of the adhesiveresin layer was varied. The peel strength and the discharge capacity areplotted against the thickness in FIG. 7. As can be seen, with a coatingthickness of 10 μm or smaller, the adhesive resin layer fills the gapformed by the unevenness of the electrode and the separator so that ahigh discharge capacity can be secured. If the thickness exceeds 10 μm,the passages for ions are so long that they become resistance and causegradual reduction of discharge capacity. If the thickness of theadhesive resin layer is increased to about 50 μm, the rate of reductionin discharge capacity is as high as about 50%.

TABLE 3 Volume of Adhesive Solid Void Peel Discharge Weight ParticleSize Matter Volume Strength Capacity Resin Filler Ratio of Filler (%)(%) (gf/cm) (1C) (mAh) Example 1 PVDF alumina 1:1 0.01 50 50 70 62Example 6 PVDF alumina 2:1 0.01 70 30 85 58 Example 7 PVDF alumina 1:50.01 30 70 60 65 Compara. PVDF alumina 10:1  0.01 90 10 100  20 Example4 Compara. PVDF alumina  1:10 0.01 10 90 20 65 Example 5

TABLE 4 Adhesive Peel Discharge Weight Particle Size Thickness StrengthCapacity Resin Filler Ratio of Filler (μm) (gf/cm) (1C) (mAh) Example 1PVDF alumina 1:1 0.01  4 50 60 Example 8 PVDF alumina 1:1 0.01  7 60 58Example 9 PVDF alumina 1:1 0.01 10 65 55 Example 10 PVDF alumina 1:10.01 20 70 50 Compara. PVDF alumina 1:1 0.01 50 70 30 Example 6

FIG. 5 shows the results obtained from different kinds of fillers. Itwas proved that various fillers produce similar effects. In particular,great effects are obtained with inorganic compounds and polymers.

TABLE 5 Adhesive Peel Discharge Weight Particle Size Strength CapacityResin Filler Ratio of Filler (gf/cm) (1C) (mAh) Example 1 PVDF alumina1:1 0.01 50 60 Example 11 PVDF silica 1:1 0.01 50 60 Example 12 PVDFsilicon 1:3 0.5 80 50 carbide Example 13 PVDF boron 1:3 0.5 80 50carbide Example 14 PVDF silicon 1:3 0.5 80 50 nitride Example 15 PVDFpolymethyl 2:1 0.5 80 50 methacrylate Example 16 PVDF iron 1:2 0.5 80 45Example 17 PVDF carbon 1:5 1 50 45

Table 6 shows the results obtained when two kinds of fillers were usedin combination. It is seen that similar effects are produced whenfillers are used in various combinations. It is understood, inparticular, that materials that contain no conducive materials showgreat effects.

TABLE 6 Adhesive Filler 1 Filler 2 Resin Average Average Discharge KindWeight Weight Particle Weight Particle Peel Capacity Kind Ratio KindRatio Size Kind Ratio Size Strength (1C) (mAh) Example 1 PVDF 1 alumina1 0.01 none 0 0 50 60 Example 18 PVDF 1 alumina 0.9 0.01 alumina 0.1 155 55 Example 19 PVDF 1 alumina 0.5 0.01 silica 0.5 0.01 50 60 Example20 PVDF 1 alumina 0.9 0.01 silica 0.1 0.5 55 55 Example 21 PVDF 1alumina 0.9 0.01 PMMA 0.1 0.5 55 55 Example 22 PVDF 1 alumina 0.9 0.01iron 0.1 0.5 55 50 Example 23 PVDF 1 alumina 0.9 0.01 carbon 0.1 1 55 50Example 24 PVDF 1 alumina 0.9 0.01 silicon 0.1 0.5 55 55 carbide Example25 PVDF 1 silicon 0.5 0.5 PMMA 0.5 0.5 80 55 carbide Example 26 PVDF 1PMMA 0.5 0.5 iron 0.5 0.5 80 45 Example 27 PVDF 1 PMMA 0.5 0.5 carbon0.5 1 80 45

Table 7 shows the results of testing on battery characteristics ofvarious battery structures. It proves that satisfactory batterycharacteristics can be obtained irrespective of the battery structure.In particular, it is seen that high-performance batteries having a highbattery capacity can be obtained when the invention is applied to alaminated battery body composed of a plurality of unit electrode bodies.

TABLE 7 Adhesive Discharge Weight Particle Size Capacity Resin FillerRatio of Filler Battery Structure (1C) (mAh) Example 1 PVDF alumina 1:10.01 tabular unit  60 electrode type Example 23 PVDF alumina 1:1 0.01tabular laminated 360 electrode type Example 29 PVDF alumina 1:1 0.01tabular laminated 360 electrode type Example 30 PVDF alumina 1:1 0.01tabular rolled 360 electrode type Example 31 PVDF alumina 1:1 0.01tabular rolled 360 electrode type Example 32 PVDF alumina 1:1 0.01tabular rolled 360 electrode type Example 33 PVDF alumina 1:1 0.01tabular rolled 360 electrode type

INDUSTRIAL APPLICABILITY

The battery according to the invention is used as a secondary battery,etc. in portable electronic equipment and has reduced size and weight aswell as improved battery performance.

What is claimed is:
 1. A battery comprising a battery body including: apositive electrode and a negative electrode each containing an activematerial; a separator holding an electrolyte; and an adhesive resinlayer joining at least one of the positive and the negative electrodesto the separator, wherein said adhesive resin layer contains aparticulate, electrically non-conductive material or semiconductor as afiller which provides passages through the resin layer through whichions pass, wherein the average particle size of the filler particles isequal to or smaller than the particle size of the active material whichconstitutes each electrode.
 2. A battery according to claim 1, whereinthat said electrolyte is an organic electrolyte containing lithium ions.3. A battery according to claim 1, wherein said average particle size ofsaid filler is 1 μm or smaller.
 4. A battery according to claim 1,wherein the sum of a volume ratio of the adhesive resin and that of thefiller per unit volume of said adhesive resin layer is less than
 1. 5. Abattery according to claim 4, wherein the sum of a volume ratio of theadhesive resin and that of the filler per unit volume of said adhesiveresin layer is 0.2 to 0.8.
 6. A battery according to claim 1, whereinsaid adhesive resin layer is constituted so as to fill the vacanciesformed in the interface between each electrode and the separator due tothe unevenness of the electrode and the separator.
 7. A batteryaccording to claim 1, wherein said battery body is a laminate of aplurality of electrode bodies each composed of a single layer of thepositive electrode, a single layer of the separator, and a single layerof the negative electrode.
 8. A battery according to claim 7, whereinsaid laminate is formed by interposing the positive electrode and thenegative electrode alternately among a plurality of the separators.
 9. Abattery according to claim 7, wherein said laminate is formed byinterposing the positive electrode and the negative electrodealternately between rolled separators.
 10. A battery according to claim7, wherein said laminate is formed by interposing the positive electrodeand the negative electrode alternately between folded separators.
 11. Abattery according to claim 1, wherein the adhesive resin layer is porousand thereby contains electrolytes which permits the resin layer toexhibit ionic conductivity.
 12. A battery comprising a battery bodyincluding: a positive electrode and a negative electrode each containingan active material; a separator holding an electrolyte; and an adhesiveresin layer joining at least one of the positive and the negativeelectrodes to the separator, wherein said adhesive resin layer comprisesa layer containing an electrically conductive filler and a layercontaining at least one of non-electrically conductive and semiconductorfiller, the fillers in the adhesive resin layer providing passagesthrough which ions pass.
 13. A battery according to claim 12, whereinthat said electrolyte is an organic electrolyte containing lithium ions.14. A battery according to claim 12, wherein that the average particlesize of said filler is equal to or smaller than the particle size of theactive material constituting each electrode.
 15. A battery according toclaim 14, wherein said average particle size of said filler is 1 μm orsmaller.
 16. A battery according to claim 12, wherein the sum of avolume ratio of the adhesive resin and that of the filler per unitvolume of said adhesive resin layer is less than
 1. 17. A batteryaccording to claim 16, wherein the sum of a volume ratio of the adhesiveresin and that of the filler per unit volume of said adhesive resinlayer is 0.2 to 0.8.
 18. A battery according to claim 12, wherein saidadhesive resin layer is constituted so as to fill the vacancies formedin the interface between each electrode and the separator which isattributable to the unevenness of the electrode and the separator.
 19. Abattery according to claim 12, wherein said battery body is a laminateof a plurality of electrode bodies each composed of a single layer ofthe positive electrode, a single layer of the separator, and a singlelayer of the negative electrode.
 20. A battery according to claim 19,wherein said laminate is formed by interposing the positive electrodeand the negative electrode alternately among a plurality of theseparators.
 21. A battery according to claim 19, wherein said laminateis formed by interposing the positive electrode and the negativeelectrode alternately between rolled separators.
 22. A battery accordingto claim 19, wherein said laminate is formed by interposing the positiveelectrode and the negative electrode alternately between foldedseparators.
 23. A battery according to claim 12, wherein the adhesiveresin layer is porous and thereby contains electrolytes which permit theresin layer to exhibit ionic conductivity.